Helioseismology: a fantastic tool to probe the interior of the Sun

Helioseismology, the study of global solar oscillations, has proved to be an extremely powerful tool for the investigation of the internal structure and dynamics of the Sun. Studies of time changes in frequency observations of solar oscillations from helioseismology experiments on Earth and in space have shown, for example, that the Sun's shape varies over solar cycle timescales. In particular, far-reaching inferences about the Sun have been obtained by applying inversion techniques to observations of frequencies of oscillations. The results, so far, have shown that the solar structure is remarkably close to the predictions of the standard solar model and, recently, that the near-surface region can be probed with sufficiently high spatial resolution as to allow investigations of the equation of state and of the solar envelope helium abundance. The same helioseismic inversion methods can be applied to the rotational frequency splittings to deduce with high accuracy the internal rotation velocity of the Sun, as function of radius and latitude. This also allows us to study some global astrophysical properties of the Sun, such as the angular momentum, the grativational quadrupole moment and the effect of distortion induced on the surface (oblateness). The helioseismic approach and what we have learnt from it during the last decades about the interior of the Sun are reviewed here.Comment: 36 page

From Creativity to Innovation in Organizations

Creativity
 is
 generally
 associated
 with
 the
 innovation
 and
 change.
 The
 most
 creative
 companies
 have
 also
 been
 the
 first
 to
 innovate
 in
 marketing
 and
 advertising,
 indiscriminately.
The
 creativity 
that
 took 
form
 depends 
on
 the 
things
to
 which 
people
 and
 businesses
 give
 value,
 in
 what
 they
 believe.
 We
 discussed
 also
 the
 nature
 of
 the
 creative
 process 
and
 ways 
to
 encourage 
and
 give
 it practical 
nature. 
We 
base d
on
t premise 
that
 the
 nature
 of
 the
 creative
 process
 is
 immutable,
 whatever
 the
 area
 in
 which
 it
 is
 applied.
 Understanding
 this
 nature,
 we
 can
 stimulate
 our
 creative
 thinking
 in
 order
 to
 obtain
 innovation,
 even
 on 
issues 
where 
the 
so‐called 
"creative" 
solutions 
are 
little 
valued.Imagination,
 Creativity, 
Innovation,
 Organization

Weyl states and Fermi arcs in parabolic bands

Weyl fermions are shown to exist inside a parabolic band, where the kinetic energy of carriers is given by the non-relativistic Schroedinger equation. There are Fermi arcs as a direct consequence of the folding of a ring shaped Fermi surface inside the first Brillouin zone. Our results stem from the decomposition of the kinetic energy into the sum of the square of the Weyl state, the coupling to the local magnetic field and the Rashba interaction. The Weyl fermions break the time and reflection symmetries present in the kinetic energy, thus allowing for the onset of a weak three-dimensional magnetic field around the layer. This field brings topological stability to the current carrying states through a Chern number. In the special limit that the Weyl state becomes gapless this magnetic interaction is shown to be purely attractive, thus suggesting the onset of a superconducting condensate of zero helicity states

Polynomial Profits in Renewable Resources Management

A system of renewal equations on a graph provides a framework to describe the exploitation of a biological resource. In this context, we formulate an optimal control problem, prove the existence of an optimal control and ensure that the target cost function is polynomial in the control. In specific situations, further information about the form of this dependence is obtained. As a consequence, in some cases the optimal control is proved to be necessarily bang--bang, in other cases the computations necessary to find the optimal control are significantly reduced

Stability and Optimization in Structured Population Models on Graphs

We prove existence and uniqueness of solutions, continuous dependence from the initial datum and stability with respect to the boundary condition in a class of initial--boundary value problems for systems of balance laws. The particular choice of the boundary condition allows to comprehend models with very different structures. In particular, we consider a juvenile-adult model, the problem of the optimal mating ratio and a model for the optimal management of biological resources. The stability result obtained allows to tackle various optimal management/control problems, providing sufficient conditions for the existence of optimal choices/controls.Comment: 22 pages, 7 figure